Need help, haven't rode in a month!

[nfriday]

First off I want to say thank you in advance for any help that is given, it is much appreciated!

I have a 1981 xs400 special 2 with stock carbs on it, I have switched over manual petcock (covered vacuum "knobs" on carb boots) with good gas flow. I am getting very good spark on both sides, correct wires to each plug. My float height is set at around 26mm. Mixture screws set and 3 1/2.

It will start and run good for a min and then act as though it is gas starved, sputter for a few seconds then die. Also while riding I can not fully let off the Throttle for it will die. I have changed float height and mixture screw numerous times. The carbs are extremely clean! I can not figure out what is wrong! I just want to ride! Please help!!!!!

 

[JARichmond]

Have a quick look at your idle set screw (not to be confused with your mix screws). It's attached to the bottom of the carbs (right in the middle) and acts as a stopper for the throttle junction. I have mine set at about 4 turns from 0 lash and it idles at around 1500 RPM.

 

[nfriday]

Sorry forgot to mention that also. I can adjust that all the way in and out with no significant change.

 

[JARichmond]

Maybe your gas cap is plugged. Will it idle alright with the cap open?

 

[nfriday]

Doesn't seem to change anything with the gas cap open :/

 

[Iggster]

could it be the petcock? I am assuming you put it to prime to start and then to on to run....could it be fouled up?

 

[Iggster]

could it be the petcock? I am assuming you put it to prime to start and then to on to run....could it be fouled up?

disregard...reread your initial post

 

[226dark]

hello everyone, I have an 81 special II and it simply will not start.
The only way I can get it started is with ether, I know this is hard on an engine so I try to stay away from it. And when it does get started it runs on one cylinder, the other sputters and backfires...
I have cleaned the carbs, changed the plugs, and also changed the battery.
I am getting good spark on both sides so I know that isn't the problem.
I have box filters and they are spotless on the inside...
Take has no rust, and I run premium in it.
I was convinced that maybe I was losing compression so I ran a test today and I have 130 on the running cylinder and 140 on the one not running.

I just simply don't kno where to go from here. Any help would be appreciated...thanks a lot

thanks alot jscgdunn,
i have them apart right now, looks like one of my needle and seats isnt working right (doesnt move freely)
also i have a mixture screw that is totally destroyed.
i am making a trip to the shop after work to order parts. ill keep you updated on my success (wishful thinking) lol

So what was the update on that?
Was gonna say possibly air starved but seems air filters are clean.
The mixture screw that was totally destroyed, is the passage now free? I would have a look.
Are the carbs synced?
When it runs for a minute then dies is that with the choke on or after it is warmed up and choke off?

 

[nfriday]

Well since then I have put new needle and seat in and also a new float. I was going to ask if you guys think that maybe a messed up pilot jet could do this? I have had the carbs apart and cleaned extremely intricately. But both of my pilot screws I couldnt get out to clean (heads stripped from PO). Do you guys have any brilliant ideas on getting them out? Salvaging them is no big deal since I have new ones to put in their place. Could this be my problem???